As a film forming apparatus for forming a thin film such as silicon oxide (SiO2) on a substrate such as a semiconductor wafer (hereinafter, referred to as a wafer), for example, a film forming apparatus for performing atomic layer deposition (ALD) has been known. As an example of this type of the film forming apparatus, there is an apparatus including a process chamber whose inside is kept in a vacuum atmosphere and in which a rotation table allowing, for example, a wafer to be loaded thereon is disposed. Above the rotation table, a gas nozzle discharging a source gas which is a raw material of, for example, a silicon oxide film, and a gas nozzle discharging an oxidation gas oxidizing the source gas are disposed. In addition, while the wafer is revolved by the rotation of the rotation table, the wafer alternately passes through an adsorption region to which the source gas is supplied and an oxidation region to which the oxidation gas is applied, thereby forming a silicon oxide film.
In ALD, in order to control the distribution of in-plane film thickness of the wafer, distribution of the source gas adsorbed onto the wafer needs to be controlled. Thus, in such a film forming apparatus, the number and locations of discharge holes formed in the gas nozzle for the source gas are suitably adjusted. In addition, selection of shapes of the gas nozzles, a regulation of a supply amount of a separation gas supplied for separating the adsorption region and the oxidation region, adjustment of concentration of a carrier gas in the source gas, and the like are suitably performed.
In a certain case, an etching rate for each of a peripheral portion and a center portion of the wafer can be adjusted by etching after a film formation process. In this case, since film thicknesses at the peripheral portion and the center portion can be aligned after the etching, a highly uniform film thickness is required particularly in a circumferential direction of the wafer. However, due to revolution of the wafer, each portion of the wafer is repeatedly moved along the same orbit separated from a rotation center of the rotation table by a predetermined distance. Thus, there can be concerns that a deviation in distribution of the source gas in an adsorption region can cause a deviation in film thickness on the wafer along a radial direction of the rotation table, and that the deviation in film thickness would not be sufficiently solved through adjustment of the discharge holes and the like as set forth above.
In the related art, a plurality of loading regions of wafers are formed on the rotation table, and the revolving wafers are rotated by a plurality of rotation devices disposed on the respective loading regions. However, installation of the plural rotation devices causes an increase in manufacturing costs of the apparatus.